package com.example.utils;

/**
 * @author 游家纨绔
 * @dateTime 2023-09-09 22:00
 * @apiNote TODO 雪花算法工具类
 */
public class SnowFlakeUtils {

	/**
	 * 起始的时间戳
	 */
	private static final long START_STMP = 1480166465631L;

	/**
	 * 每一部分占用的位数
	 */
	private static final long SEQUENCE_BIT = 12;  // 序列号占用的位数
	private static final long MACHINE_BIT = 5;    // 机器标识占用的位数
	private static final long DATACENTER_BIT = 5; // 数据中心占用的位数

	/**
	 * 每一部分的最大值
	 */
	private static final long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
	private static final long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
	private static final long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

	/**
	 * 每一部分向左的位移
	 */
	private static final long MACHINE_LEFT = SEQUENCE_BIT;
	private static final long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
	private static final long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

	private static long datacenterId = 7;   // 数据中心
	private static long machineId = 7;      // 机器标识
	private static long sequence = 0L;      // 序列号
	private static long lastStmp = -1L;     // 上一次时间戳

	public SnowFlakeUtils(long datacenterId, long machineId) {
		if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
			throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
		}
		if (machineId > MAX_MACHINE_NUM || machineId < 0) {
			throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
		}
		SnowFlakeUtils.datacenterId = datacenterId;
		SnowFlakeUtils.machineId = machineId;
	}

	/**
	 * 产生下一个ID
	 */
	public synchronized static long nextId() {
		long currStmp = System.currentTimeMillis();
		if (currStmp < lastStmp) {
			throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
		}

		if (currStmp == lastStmp) {
			// 相同毫秒内，序列号自增
			sequence = (sequence + 1) & MAX_SEQUENCE;
			// 同一毫秒的序列数已经达到最大
			if (sequence == 0L) {
				currStmp = getNextMill();
			}
		} else {
			// 不同毫秒内，序列号置为0
			sequence = 0L;
		}

		lastStmp = currStmp;

		return (currStmp - START_STMP) << TIMESTMP_LEFT // 时间戳部分
				| datacenterId << DATACENTER_LEFT       // 数据中心部分
				| machineId << MACHINE_LEFT             // 机器标识部分
				| sequence;                             // 序列号部分
	}

	private static long getNextMill() {
		long mill = System.currentTimeMillis();
		while (mill <= lastStmp) {
			mill = System.currentTimeMillis();
		}
		return mill;
	}

	public static void main(String[] args) {
		for (int i = 0; i < (1 << 12); i++) {
			System.out.println(SnowFlakeUtils.nextId());
		}

	}
}
